二酸化炭素冷凍サイクル用膨張機内の漏れ流動特性

抄録

  Carbon dioxide (CO₂) is considered to be an alternative to HFC refrigerants due to its non-flammability, non-toxicity and small global warming potential. To improve the performance of the CO₂ refrigeration cycle, using an expander as an expansion device to recover a throttling loss has been examined.
  Since an inlet condition of the expander is supercritical and an exit is subcritical, leakage through a narrow clearance in the expander becomes a transcritical flow where the condition changes from the supercritical to the subcritical. It is necessary to clarify the characteristics of the transcritical leakage flow through the narrow clearance, because the leakage flow has serious influence on the expander performance. In this study, the transcritical leakage flow is modeled analytically and the flow characteristic is examined by the model. The calculated mass flow rate agrees with the experimental one. It is found that frictional loss accounts for a half of pressure drop both in the supercritical and two phase region at any inlet temperature tested in this study. In addition, the sealing effect of oil on the transcritical leakage flow rate is shown to be little.